Ultra high frequency wave generator



Dec. 12, l950 LE ROY AMER ETAL ULTRn HIGH FREQUENCY WAVE GENERATOR Filed June 25, 1945 2 Sheets-Sheet l e, T V/ QN b S 6M e mii, Y Yu @MKM w Q m K t yh t /Whnmlvu/u/H m. NL l E bn e O a,C MVM/MM/ W W VCH n. W ,/m a n.. C W h w m L o .n E l A b mm a. V 1.a gmwm@ xi ww n m. sv ..s N ww mw Wsw ww m\l .mmm f A WS wm. .w w W, .w li, 1 Y im.; EEES:`mSm vlm\\H| Il Il lwl w 1 f Dec. 12, i950 LE ROY APKER ET A1. 2,534,098

ULTRA HIGH FREQUENCY WAVE GENERATOR Filed June 25, 1945 2 Sheets-Sheet 2 Figli.

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l idw l a l [d Inventors;

Le Roy Apker, Joseph Kahnke,

Patented Dec. 12, 1950 ULTRA HIGH FREQUENCY WAVE GENERATOR LeRoy Apker, Niskayuna, andJoseph Kahnke,

Schenectady, N. Y., assignors to General Electrio Company, a corporation of New York Application June 23, 1945, Serial No. 601,125

(Cl. 25o-37) 13 Claims.

Our invention relates to ultra high frequency apparatus and has as its primary object to provide a new and improved meter for measuring the frequency of ultra high frequency waves.

In the copending application of LeRoy Anker, Serial No. 601,124, led June 23, 1945, now Patent No. 2,518,113, and assigned to the same assignee as the present invention, there is disclosed apparatus for analyzing ultra high frequency waves to determine the frequency or spectrum of such waves which enploys a variable oscillator to provide a wave which may be compared visually by means of a cathode ray tube with a received wave. The received waves are variable over a wide frequency range and the frequency of the oscillator is variable over an equal range of megacycles, the average range of the oscillations being considerably higher than that of the received waves Whose frequency is to be determined. It has been found that, in analyzing ultra high frequency Waves with such or similar apparatus, the determination of the frequency of the output Wave of the variable oscillator with sufli-v cient accuracy presents a major problem. Thus,

where it is desired to analyze waves in the range of, for example, from 500 to 4000 megacycles by a single tuning operation, heretofore there has not been available an ultra high frequency source variable over this range. When a higher frequency oscillator is employed which covers the same number of megacycles in a higher frequency range, recourse must be had to some additional means for measuring the frequency of such an oscillator before the frequency characteristics of the received wave can be determined With suiiicient accuracy.

It is an object of our invention to provide a new and improved Wavemeter for use with an ultra high frequency spectrum analyzer for measuring the frequency of a received Wave.

It is another object of our invention to provide a new and improved ultra high frequency pulse generator.

It is a further object of our invention to provide a new and improved variable ultra high frequency pulse generator characterized by its provision of a relatively uniform power output over a wide frequency range.

It is a still further object of our present invention to provide a new and improved means for exciting a cavity resonator.

It is still another object of our invention to provide an easily adjusted variable ultra high frequency pulse generator which provides a suflil) ciently strong output signal over a wide frequency range to facilitate analysis of ultra high frequency spectra.

It is a still further object of our invention to provide a new and improved spark exciter.

It is still another object of our invention to provide a new and improved generator for supplying impulses to a Wave transmission system.

One of the features of our invention is the employment in an ultra high frequency wavenieter of a cavity resonator of variable dimensions excited by a spark gap to produce an ultra high frequency Wave, the frequency of which is variable and accurately determinable.

For a better understanding of our invention, reference may be had to the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims. Fig. l is a longitudinal sectional view of a wavemeter suitably embodying the invention; Fig. 2 is a transverse sectional view taken along the line 2-2 of Fig. 1; Fig. 3 is a portion of a longitudinal sectional view taken along the line 3 3 of Fig. 2; Fig. 4 illustrates diagrammatically an ultra high frequency spectrum analyzer embodying the wavemeter of Fig. l and Figs. 5 and 6 illustrate schematically modifications of our invention for determining resonance points in broad band transmission systems,

Referring to Fig. l, we have there illustrated the wavemeter as comprising a cavity resonator l of the concentric conductor type and a mechanism 2 for varying the dimensions of the cavity resonator. The cavity is excited by an exciting means 3 to supply a wave of variable frequency to an indicating meter it, the frequency of the Wave being indicated by a suitable measuring means 5.

The cavity resonator l comprises a centrally positioned inner conductor G and a tubular outer conductor l which are short-circuited at one end by means of an end wall 8 and a plurality of resilient fingers connected to the end wall 8 and engaging the outer surface of conductor S. An end wall l@ closes the opposite end of the resonator and supports within the resonator a stub conductor ii of the same outer diameter as the conductor 6 and separated from the adjacent end of the conductor 5 by a gap l2 which is adjustable in length in a manner to be described later. Preferably, the conductors (i, 'l and the stub conductor H are formed of a good conductive metal, such as copper or silver. The end wall lll may be attached to the cuter con- 3 ductor l by means of screws i3 and the stub conductor li may similarly be supported from the end wall ii by a screw Effi. At the opposite end of the cavity resonator, the end wall il is provided with a flange l5 which overlies a flange le connected to the outer conductor and is clamped thereto by means or" a plurality of screws El. As thus constructed, the cavity resonator i comprises an open-ended quarter wave length resonant transmission line.

The mechanism 2 for adjusting the position of inner conductor within the cavity resonator l to adjust the dimensions of the resonator coniprises a piston i8 secured to the external end of conductor and having a threaded transverse hole i9 which engages the threads on a longitudinal screw 2li. |The piston i8 is movable longitudinally within a, cylinder 2l, which is illustrated as of the same dimensions as the outer' conductor 'E and is coaxially aligned with the outer conductor '1. One end of the cylinder 2i is attached to the end wall 8 by means of a plurality oi screws 22 and its other end is closed by an end wall 23. The screw 2li is provided with bearing surfaces 24, 25 at its opposite ends which are journalled, respectively, in the end walls 8, 23 and which permit rotational but prevent axial motion of the screw 2E?. In addition to the threaded aperture i9, the piston I8 is provided with a transverse opening 26 through :1s

which passes a guide rod 2l, the guide rod 2l being supported also by the end walls S, 23. The position oi the piston i3 and, consequently, of the inner conductor 5 may be adjusted by means of an externally accessible adjusting means, such as a knob 2t, which is attached to the external end of the screw member Z. The position oi the piston i8 within the cylinder 2i and the dimensions of the gap l2 may be measured by means of an indicating means 5 which comprises a pointer 23 which cooperates with a, scale 3Q and is connected by means of any suitable gear arrangement (not shown) or similar connecting means with a drum 3i attached to the external end of the screw 2Q and actuated by the knob 2t. The scale 3Q may indicate directly the resonance frequency of the resonator i as the length of the open-ended quarter wave length transmission line ii, 'e' is varied.

Means are provided to prevent blacklash in the adjusting of the piston i8 by means of the screw 2t and comprises a follow-up piston 32 which likewise is in threaded engagement with the screw 2e and which is resiliently biased with respect to the piston i3 by a plurality of spring members 33. The structure of this portion of the mechanism 2 may best be seen by reference to Figs. 2 and 3 in which the follow-up piston and the piston E8 are shown as slidable along the guide rod 2l' and engaging the threads of screw 2S.

The means 3 for exciting the cavity resonator l comprise a spark gap 3d formed by a pair of electrodes 35, Se of a suitable metallic material, such as tungsten, the electrode 35 being connected by a conductor 3l to an input electrode or coupling loop 3B which extends into the cavity resonator l. While the input electrode 38 has been illustrated as a coupling loop, any other suitable exciting electrode means may be employed. The conductor 3l is supported by an insulator 39 which is contained within a, sleeve member Il@ which passes through housing member lll supported Within a lateral opening in the conductor 1. The housing member e! is externally threaded to engage a cap 42 to support the sleeve lo and the electrode 35 in the desired position. The sleeve lil?, at its end remote from the resonator l, is provided with external threads i3 which engage cooperating threads within a metal tube ld and which provide means for adjusting the length of gapl 3G. The electrode 3S is supported from a cylindrical conductive plug te which lies within the tube dii, being insulated therefrom by means of a tubular insulator 6E. The insulator it may be formed of any suitable low loss insulating material, for example polystyrene or a vitreous material, and is provided at one end with a solid portion il through which extends a screw d8 which engages the plug 35 and forms a conductive connection between that plug and a resistor 59 supported within the tube fili. rhe resistor i9 may be of any suitable type, for example a conventional carbon resistor. At one end, the resistor is connected to the screw i3 and at its opposite end, to a female contact 5! which is insulatingly supported within a closure member 5l by means of an insulator 52. The closure member el may be secured to the end of the tube dfi by screws 53. The female contact provides means for connecting the resistor e9 to a suitable source of unidirectional voltage of high value, represented conventionally as the battery 5d, the opposite end of the battery being grounded.

in the construction or" the exciting means 3, the spark gap Se is placed as close as possible to the cavity resonator, and is connected thereto by a very short length of conductor 3l, so that the inductance or" the conductor 3l between the gap and the loop 33 is a minimum and the voltage across the loop 33 is a maximum. The plug 5, in cooperation with the tube 44 and the insulator d, forms a shunt capacitance which is charged through the resistance 39 by the high tension unidirectional source 5G until the voltage between the electrodes 35, Se is sunlcient to cause a breakdown of the gap 34 to produce a discharge between the electrodes. Since the spark gap is placed as close as possible to the input electrode 3S, a maximum pulse of exciting voltage due to a current pulse passing through the loop 38 is provided Within the resonator l to produce, by shock excitation, oscillations oi E a frequency determined by the position of the inner conductor that is, by the dimensions of the cavity resonator. The coupling is effected by coupling the electromagnetic eld oi the loop 33 to the cavity at an optimum position therein to establish electromagnetic waves of a frequency determined by the dimensions of the cavity. The resistance @9 is effective to attenuate any back fpulse of high frequency voltage. Means are provided for by-passing to ground any ultra high frequency wave which travels outwardly from the cavity resonator I along the elements within the tube fili and comprises 9, capacitor 5Fl connected between the conductor connected with the con tact and ground.

Means are provided for supplying energy from the cavity resonator E to the meter Il and comprise any suitable output electrode means which may be, for example, a coupling loop Coupling loop 55 is connected at one end to a tubular plug 5S provided in a lateral opening in the outer conductor l to form with a tubular connecting member 5l the outer conductor of a noneresonant concentric transmission line connected between the resonator I and the meter A wire 58 connected to the coupling loop 55 forms the inner 'of the incoming wave.

conductor of this" li-ne. Preferably, the output line 51, 58 is non-resonant in character so that it has a fiat impedance versus frequency characteristic.-

The operation of the wavemeter described above may best be explained by reference to the spectrum analyzer shown in block diagram in Fig. 4. This spectrum analyzer may be of the type shown in the above-mentioned copending application of LeRoy Apker or it may be any other suitable spectrum analyzer. In the analyzer of Fig. 4, which is of the type shown in the above-mentioned application of LeRoy Apker, the received wave whose frequency is to be determined is transmitted from an input source, such as an antenna 59, Vthrough a high frequency choke 60 to a high frequency mixer El where it is combined with a locally produced ultra high frequency oscillation from a variable ultra high frequency oscillator 62. A lter E3, interposed between the mixer 6l and the oscillator 62, provides means to prevent reflection to the oscillator 52 of Waves of the mixed frequency obtained through the mixing action of the mixer 6I. The constant frequency output wave of the mixer 63 is supplied through a tunable ultra high frequency filter 6G to a second mixer 65 where this constant frequency signal is combined With a second locally produced oscillation of fixed frequency provided by an oscillator 66 and supplied to the mixer 35 through a pairof tunable ultra high frequency filters 6l, $8. The mixer 65 combines the two ultra high frequency oscillations provided by the oscillator 66 and the mixer 6l to form a constant, relatively low frequency wave which is supplied through a high frequency choke 69 to an output device which lnay be, for example, a cathode ray oscilloscope 10.

In a spectrum analyzer of this type, where it is desired to measure input Waves which vary over a substantial frequency range, it has been found extremely difficult to provide any means actuated by the control utilized to vary the oscillations of oscillator 62 to provide an accurate indication of the frequency of such oscillations. Of course, the accuracy of the analyzer in determining the frequency of a wave supplied to the antenna 59 is dependent upon the accuracy o1 the means used to determine the frequency of the Wave of the oscillator B2. Our invention provides such an accurate frequency determining means and, in Fig. 4, the shock excited cavity resonator .l is illustrated as connected by means of conductor 58 through a decoupling resistor H to the input side of the choke B0.

In the operation of the analyzer of Fig. 4 employing the Wavemeter of our invention, the oscillator 62 is varied over a range of ultra high frequency waves to provide oscillations which are combined in mixer 6| with an input signal, whose frequency may vary over a Wide range, supplied to the antenna 59 until a constant frequency Wave of the frequency to which the filter 64 is tuned is provided. This constant ultra high frequency wave, in turn, is combined in mixer t5 with the constant ultra high frequency wave from oscillator `66 to provide a relatively low constant frequency Wave which gives an indication on the cathode ray oscilloscope 10. The dimensions of the cavity resonator l are varied by changing the length oi the inner conductor 6 by means of the control knob 28 until a pulse of oscillations is provided, the frequency of which is the same as that This condition is indicated by the production on the cathode ray oscilloscope of a pulse of deflections.

The spark exciter described above is useful also for determining resonant points in a broad band transmission system or in other circuits.

Particularly when used in conjunction with a spectrum analyzer to cover the intended transmission range, small variations of Q in such a broad band transmission system may be detected. In the modification of the invention of Fig. 5, our improved spark exciter 3 is shown as being connected by the output conductor 31 to the inner con-ductor l2 of a coaxial transmission line having a tubular outer conductor 13. The transmission line 72, 'I3 may be of conventional form and our improved spark exciter is useful in studying the transmission characteristics of this line to determine any resonance points of the line. The outer conductor 'I3 is grounded so that the wave of the spark exciter 3 is applied between the inner and outer yconductor of the transmission line. At the opposite end of the line, the inner and outer conductors are connected to means for measuring the energy transmitted over the line at different frequencies. Such measuring means may be, for example, a spectrum analyzer 14 which employs an indicating instrument 15. The analyzer 'I4 may be of the type shown in Fig. 4 or of any other suitable type. Since the Wave transmitted from the spark exciter 3 has frequency components from very low to very high frequencies, with the use of the analyzer 74 andthe indicating instrument 15, the apparatus of Figi 5 is useful to detect the transmission through the line l2, 13 at all frequencies in the range and give an indication of any increase in Q of the transmission system at any particular frequency of the range.

In the modification of Fig. 6, the spark exciter 3 is shown as connected to a wave guide system to determine the transmission characteristics of this system. The output conductor 31 of the exciter is extended across one end of the Wave guide 16 to form an input electrode l?. The Wave guide I6 may contain a plurality of discontinuities, such as the radial resonators 18, 19. The transmission characteristic of the wave guide system may be determined by connecting a spectrum analyzer 8i) to an output electrode 8i connected across a distant point of the guide, for example, near the opposite end of the guide. rThe analyzer 86 preferabiy includes an indicating instrument 82 of the visual type to show any increase in transmission of energy at the particular frequency. It is apparent, of course, that the spark exciter may likewise be employed with a cavity resonator or any other type of transmission system. In each instance, the exciter functions as a low. internal impedance generator to supply impulses to the systems, these impulses having a Wide frequency spectrum so that the exciter is useful in analyzing broad band transmission systems which are to carry either low or high frequencies. An important advantage of the exciter is that it is capable of withstanding high voltages and supplying useful amounts of energy to a system to be studied.

Another important advantage of our invention is that it provides a high Voltage excitation of the cavity resonator I, especially when spark gap 34 is located as close as possible to the input to the cavity resonator. Another advantage is that the invention provides a variable frequency pulse generator which gives a high intensity output signal at all frequencies over a very Wide band. The repetition rate is controlled by the values of the resistor 49 and the capacitor formed by the members 'i4-4t. Thus, in one construction according to our invention, the output frequency was variable over a range of 500 to 3560 megacycles, the output signals being pulsed at a repetition rate of approximately 20 kilocycles per second. Over this wide frequency band, the output signals were of sufficiently high intensity and of relatively uniform value that they provided a good Calibrating means for the analyzer.

, Another important advantage of our invention is that the generator for ultra high frequencies which varies over a wide range is adjustable by a very simple control means.

While the invention has been described by reference to a particular embodiment thereof, it will be understood that numerous modifications may be made by those skilled in the art without departing from the invention. We therefore aim in the appended claims to cover all such equivalent variations as come within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States, is:

1. A pulse generator comprising a cavity resonator having an input electrode and an output electrode, a spark gap connected to said input electrode, means for supplying a unidirectional potential to said spark gap, and a capacitance connected between said last means and said gap whereby repeated pulses of exciting potential are supplied to said resonator.

2. A generator for providing ultra high frequency waves comprising a cavity resonator having an input electrode and an output electrode, a spark gap serially connected with said input electrode external to said resonator, means adapted to supply a unidirectional potential to said gap, and a capacitance connected between said means and said gap, said resonator being adjustable in dimension whereby pulses of ultra high frequency signals variable over a wide frequency range are supplied to said output electrode.

3. In a wavemeter for ultra high frequency signals comprising a cavity resonator having an input electrode and an output electrode, said resonator comprising a tubular outer conductor and a centrally disposed axially positionable inner conductor, said resonator having an end wall and said inner conductor having one of its ends in variable spaced relation with said end wall, a spark gap connected to said input electrode external to said resonator, means adapted to supply unidirectional potential to said gap, a cap-acitance connected between said last means and said gap, means for varying the spacing between the end of said inner conductor and said end wall to Vary the resonance frequency of said resonator, and means connected with said last means for indicating the resonance frequency of said resonator.

4. In combination, a cavity resonator comprising a tubular outer conductor1 and a centrally disposed inner conductor, said resonator having an end wall connected across said outer conductor and said inner conductor having one of its ends in spaced relation with respect to said end wall, means for exciting said resonator comprising an input electrode extending into said resonator through a lateral opening in said outer conductor, a spark gap serially connected with said input electrode, means adapted to supply high voltage unidirectional potential to said gap, a capacitor connected between said last means and said gap, output electrode means connected with said resonator, and means for adjusting the spacing between the end of said inner conductor and said end wall to vary the resonance frequency of said resonator whereby high frequency waves variable over a wide range are supplied to said output electrode.

5. An ultra high frequency pulse generator comprising a cavity resonator having an input electrode and an output electrode, said resonator being defined by al' closed metallic member and said input electrode extending through a lateral opening in said member, a tubular conductor connected with said lateral opening, a pair of spark electrodes supported within said tubular conductor, one of said spark electrodes being connected with said input electrode, a centrally positioned conductor connected with the other of said spark electrodes, insulating means interposed between said centrally positioned conductor and said tubular conductor to form a capacitance connected between said other spark electrode and said metallic member, resistance means supported within said tubular conductor and serially connected at one end with said centrally positioned conductor, and means adapted to supply unidirectional potential to the other end of said resistance means whereby pulses of high intensity current are supplied to said input electrode.

6. An ultra high frequency pulse generator comprising a cavity resonator having an input electrode and an output electrode, said resonator being defined by a closed metallic member and said input electrode extending through a lateral opening in said member, a tubular conductor connected with said lateral opening, a pair of spark eiectrodes supported within said tubular conductor, one of said spark electrodes being connected with said input electrode, a centrally positioned conductor connected with the other of said spark electrodes, insulating means interposed between said centrally positioned conductor and said tubular conductor to form a capacitance connected between said other spark electrode and said metallic member, resistance means supported within said tubular conductor and serially connected at one end with said centrally positioned conductor, means adapted to supply unidirectional potential to the other end of said resistance means, and a by-pass capacitance connected between said other end and said tubular conductor whereby pulses of high intensity current are supplied to said electrode to establish high frequency electromagnetic waves in said resonator.

7. A generator of electric pulses having a broad frequency characteristic comprising a tubular conductive member, a spark gap supported within said member and insulated therefrom, an output electrode means connected to one terminal of said gap, a capacitance supported within said member and connected between the other terminal of said gap and said member, and means adapted to impress a unidirectional potential between said capacitance and said member.

8. A generator of electric pulses having a broad frequency characteristic comprising a tubular conductive member, a spark gap supported within said member and insulated therefrom, an output electrode means connected to one terminal of said gap, a capacitance supported within said member and connected between the other terminal of said gap and said member, a resistance supported within said member and having one of its terminals connected to said capacitance,

and means adapted to supply unidirectional potential to the other terminal of said resistance.

9. A wave generator comprising a cavity resonator, a spark gap, means for energizing said spark gap, means for coupling the output energy of said spark gap substantially directly to said cavity resonator, and means for tuning said cavity resonator.

10. An arrangement according to claim 9 13. An arrangement according to claim 12 further comprising `a transmission line stub coupled in parallel with said cavity resonator substantially at its open end.

LE ROY APKER. JOSEPH KAHNKE.

REFERENCES CITED The following references are of record in the wherein said cavity resonator comprises a coaxial l0 fue of this patent:

cavity resonator, and said means for coupling comprises an electrode.

11. An arrangement according to claim 10 wherein said spark gap is energized periodically to produce a pulsed output.

12. An arrangement according to claim 9 wherein said cavity resonator comprises a coaxial cavity resonator substantially a quarter Wavelength long, a load circuit coupled to one end of said cavity resonator, the other end of said cav- 20 ity resonator being open circuited.

UNITED STATES PATENTS 

